Recently, in production of a defect-free crystal of a silicon single crystal, it comes to be essential to pull a crystal in a crystal diameter and a crystal pulling rate just as they are targeted. In the conventional diameter control of a silicon single crystal, crystal pulling is carried out by setting a base value of heater power on the basis of result data of heater power values in the previous crystal pulling, and by raising the heater power value relative to the set heater power value when the crystal diameter in the crystal pulling is thicker than the target or the crystal pulling rate is faster than the target, or reducing the heater power value in the opposite case, thereby controlling the heater power value.
In these conventional diameter control, however, the heater power is altered after the crystal diameter is varied from the target value or after the crystal pulling rate is varied from the target value. Accordingly, it wastes long period of time to change the temperature of the interface of the crystal growth, this time takes 30 minutes or more particularly in a large-diameter crystal, thereby having a problem of being too late to give feedback to heater power from a crystal diameter or a crystal pulling rate.
Moreover, a removed heat quantity from the chamber varies due to the depth of raw material melt in a quartz crucible, the length of a growing crystal, a positional relationship of each graphite material in a chamber, and an adhesion situation of oxide on the surface of a chamber of a single crystal producing apparatus, and the optimum value of heater power also varies thereby. Accordingly, it has been difficult to set the optimum value of heater power on the basis of result data of previous crystal pulling.
As an art to control a diameter on the basis of data other than the crystal diameter or the crystal pulling rate, Patent Document 1 and Patent Document 2 disclose arts in which a crystal pulling rate is given feedback on a removed heat quantity from a chamber by cooling water. These arts, however, have a problem of being difficult to pull a single crystal in a target pulling rate or a target crystal diameter when the heater power value is deviated from the optimum value.